Heredity (2008) 100, 526–532
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ORIGINAL ARTICLE
www.nature.com/hdy
Patterns in genetic diversity of Trifolium pallescens
populations do not reflect chronosequence on
alpine glacier forelands
C Raffl1, R Holderegger2, W Parson3 and B Erschbamer4
Institute of Ecology, University of Innsbruck, Innsbruck, Austria; 2WSL Swiss Federal Research Institute, Birmensdorf, Switzerland;
Institute of Legal Medicine, Innsbruck Medical University, Innsbruck, Austria and 4Institute of Botany, University of Innsbruck,
Innsbruck, Austria
1
3
How does genetic diversity within populations of plants
develop during primary succession on alpine glacier forelands? Theory predicts that pioneer populations are characterized by low genetic diversity due to founder effects and
that genetic diversity increases within populations as they
mature and recurrent gene flow occurs. However, few genetic
studies have so far been carried out on plants on glacier
forelands. In this study, we analysed the development of
genetic diversity with time for populations of Trifolium
pallescens along successional series (chronosequences) on
three parallel glacier forelands in the European Alps, using
neutral amplified fragment length polymorphism. No general
trend in the development of genetic diversity was observed
with increasing population age: even pioneer populations
harboured substantial genetic diversity. Assignment tests
showed that the latter consist of a genetic sub-sample from
several source areas, and not just from other populations on
the glacier forelands. We also detected some long distances—that is, inter-valley gene flow events. However, gene
flow was not spatially unrestricted, as shown by a weak
isolation by distance pattern within glacier valleys. The actual
patterns of genetic diversity along the chronosequences are a
result of the combination of factors, such as gene flow and
growth rate, influenced by site- and species-specific attributes.
Heredity (2008) 100, 526–532; doi:10.1038/hdy.2008.8;
published online 13 February 2008
Keywords: AFLPs; assignment test; colonization history; recent gene flow; primary succession
Introduction
Nature occasionally provides ideal situations to study
changes in genetic structure and diversity that occur as
populations grow and mature from founders. Such
opportunities are often associated with situations where
new habitat is formed and subsequently colonized by
plants (Miles and Walton, 1993). They allow the sampling
and genetic analysis of individuals from populations at
different maturation stages along time series. Glacier
forelands left by the retreat of permanent ice provide a
corresponding situation, since they exhibit different
moraines forming a spatial chronosequence. The substrate of these moraines has been exposed from ice and
thus become available for plant growth for different time
periods (Matthews, 1992).
On glacier forelands, each plant species has an
optimum point along the time series, forming a sequence
from early to late successional species. The genetic
diversity of colonizing populations of both, early- and
late-successional plant species, is highly affected by the
number of immigrating seeds and the rates of seedling
establishment (Eriksson, 1989). The latter are known to
Correspondence: Dr C Raffl, Institute of Ecology, University of Innsbruck,
Technikerstrasse 25, 6020 Innsbruck, Austria.
E-mail: [email protected]
Received 15 June 2007; revised 16 January 2008; accepted 18 January
2008; published online 13 February 2008
be low on early successional stages (NiederfrinigerSchlag and Erschbamer, 2000). On newly deglaciated
terrain, that is, the pioneer situation, available safe sites
for colonization by seed only represent a small proportion of the open area. As succession proceeds, vegetation
cover increases and ameliorates the conditions for
further seedling establishment (Stöcklin and Bäumler,
1996). As time passes, population densities of pioneer
species increase and additional species of later successional stages immigrate.
While there are comprehensive studies of the changes
in species composition during primary succession on
glacier forelands (for example, Whittaker, 1993; Frenot
et al., 1998; Mizuno, 1998), the development of genetic
diversity of colonizing populations along chronosequences on glacier forelands is less investigated. Few
genetic studies have been carried out on glacier forelands
so far (Jumpponen, 1999; Pluess and Stöcklin, 2004; Raffl
et al., 2006a). The expectations for the development of
genetic diversity within populations during primary
succession are laying along a continuum (Whitlock and
McCauley, 1990), as a combination of effects influences
the development of diversity during colonization. Genetic diversity is supposed to be low in pioneer stages
because of founder events, since the earliest populations
are founded by a few individuals (McCauley et al., 1995;
Austerlitz et al., 1997). With ongoing succession, subsequent gene flow, in plants by either pollen or seeds,
is expected to introduce new gene alleles into local
Colonization of alpine glacier forelands
C Raffl et al
527
populations. This introduction entails increasing genetic
diversity in time during the initial colonization phase.
Subsequently, diversity may decrease when gene flow
between the newly established populations creates
homogenization, and increase again, potentially reaching
its maximum in long-established populations at the
ecological optimum along the successional chronosequence (Slatkin, 1977; Loveless and Hamrick, 1984; Giles
and Goudet, 1997). The effectiveness of gene flow on
genetic diversity of local populations after establishment
over time is constrained by the diversity of source
populations, the proportion to which they contribute to
the migrant gene pool and the population growth rates
(Whitlock and McCauley, 1990; Austerlitz et al., 1997).
Genetic differentiation between colonizing populations
strongly depends upon how colonizing populations are
formed and upon the quantitative relationship between
the number of colonists founding new populations and
the number of individuals exchanged between populations (Wade and McCauley, 1988). Since colonization
takes place by a subset of seeds from potential source
populations, genetic differentiation between newly established populations is supposed to be large. However,
sub-sequential gene flow might well level out these
population structure in time.
We chose Trifolium pallescens to investigate the formation
of genetic diversity along chronosequences on alpine
glacier forelands, as it is a characteristic plant species of
this habitat type in the European Alps. The species mainly
occurs on the moraines of glacier valleys and is almost
absent from valley slopes and surrounding mountain
ridges. It thus forms an ideal study species to investigate
the genetic development of populations during primary
succession. We aimed to (1) investigate the genetic diversity
of T. pallescens populations along the chronosequence and
(2) identify potential source populations of founders
colonizing the pioneer sites of glacier forelands. Populations from three parallel alpine glacier valleys were
investigated using amplified fragment length polymorphism (AFLP) markers (Vos et al., 1995), since they provide a
fast and reliable assessment of intra-specific genetic
variability and structure (Gaudeul et al., 2000).
glacier
snout
1858
GB
1996
1923
1872
RM
glacier
snout
NE
SW2 SW1 1996
1923
NE
mountain ridge
1872
Study sites and sampling
We sampled T. pallescens from three parallel, north-west
exposed glacier valleys located above timberline (2200–
2500 m above sea level) in the upper Ötztal (Tyrol,
European Central Alps), that is, Gaisberg (GB; 461500 N,
111030 E), Rotmoos (RM; 461490 N, 111020 E) and Langtal
(LT; 461480 N, 111000 E). The mountain ridge between GB
and RM (Hohe Mut, 2670 m above sea level) was
comparatively low with alpine grasslands to the top
(Raffl and Erschbamer, 2004), while RM and LT were
separated by a high, partly glaciated mountain ridge
(Seelenkogel, 3420 m above sea level; Figure 1). The GB
valley was delimited by steep valley walls on both sides.
In the RM valley, the north-east (NE) facing slope was
also steep, while the south-west (SW) facing slope was
smoothly inclined. The LT valley was a typical U-shaped
mountain ridge
1923
Study species
T. pallescens Schreb. is a diploid (2n ¼ 16) perennial
species, known to be self-compatible, but mainly outbred
and predominantly pollinated by hover flies (Hilligardt,
1993). It shows procumbent vegetative growth forming
mats of about 10–15 cm in diameter. According to
herbchronology, the oldest plants detected so far were
about 11 years old (Kuen and Erschbamer, 2002). T.
pallescens is a subalpine to alpine species found in Central
and Southern Europe at altitudes between 1800 and
2700 m above sea level. Its main habitat are glacier
forelands, but it also occurs along river banks, on moist
scree slopes and in scarce alpine meadows on acidic
bedrock (Weber, 1979). The relatively large T. pallescens
seeds mostly germinate in the vicinity of mother plants
(Niederfriniger-Schlag and Erschbamer, 2000), rarely
reaching distances of about 6 m. The dry flower heads
are easily blown away by wind (Stöcklin and Bäumler,
1996), but almost nothing is known about the species’
potential of long-distance dispersal. T. pallescens forms a
persistent seed bank, where seeds remain viable for at
least 5 years (E Schwienbacher, unpublished data).
glacier
snout
mountain ridge
mountain ridge
SW 1996
Materials and methods
LT
1858
1858
Figure 1 Sampling locations of populations of Trifolium pallescens (open circles) on three glacier forelands in the Central European Alps. 1996,
1923, 1872 and 1858: dates of moraine stages along the chronosequences; SW: south-west exposed valley slopes; NE: north-east exposed
valley slopes; GB: Gaisberg valley; LT, Langtal valley; RM, Rotmoos valley. Airline distance between GB and RM is 1.4 km, and between RM
and LT 3.9 km.
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Colonization of alpine glacier forelands
C Raffl et al
528
DNA extraction and AFLP fingerprinting
Total genomic DNA was extracted from 5 mg of dried
plant tissue according to the CTAB protocol described by
Doyle and Doyle (1987) with minor modifications as
described by Schönswetter et al. (2002). DNA content
was quantified with a fluorescent microplate reader
(fmax 110, Molecular Devices Inc., Chicago, IL, USA)
using PicoGreen dsDNA quantification reagent (Molecular Probes, Leicten, The Netherlands) following Juen
and Traugott (2005).
The AFLP procedure was performed as described by
Schönswetter et al. (2004), and PCR amplifications were
carried out on a gradient Mastercycler (Eppendorf,
Hilden D, Germany). The following primer combinations
were used in selective amplification: EcoRI-ACA/MseICAT, EcoRI-AAG/MseI-CTT and EcoRI-AAC/MseICAGG. The fluorescence-labelled products, together
with an internal size standard (ROX-500, Applied
Biosystems, Foster City, CA, USA), were separated on
an automated capillary sequencer (ABI3100, Applied
Biosystems) and analysed using GENESCAN (Applied
Biosystems). The scoring and assembly of fragments in
the presence/absence of matrix was conducted with
GENOGRAPHER 1.6.0 (http://hordeum.msu.montana.
edu/genographer/).
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Statistical analyses
All statistical analyses were based on polymorphic loci
only. Genetic diversity within populations was quantified as average gene diversity Ha (index of average
differences; Kosman, 2003) using ARLEQUIN 1.1. Spearman’s rank correlations were calculated between moraine age (that is, time series) and average gene diversity
Ha using SPSS 13.0 (SPSS; leaving out populations from
valley slopes).
Analyses of molecular variance (AMOVA) were
carried out with ARLEQUIN 1.1 (Schneider et al., 1997)
at two different hierarchical levels, that is, among valleys
and among successional stages, that is, moraine age (thus
leaving out populations from valley sides in the latter
analysis). To test for isolation by distance (Slatkin, 1993),
matrices of direct-line geographic distances and genetic
distances (pairwise FST-values from AMOVA) were
correlated in a Mantel test using ARLEQUIN 1.1 with
1000 permutations for significance testing. Isolation by
distance was determined for the whole data set and for
each valley, separately.
Recent gene flow (Manel et al., 2005) to the 1996
pioneer situation was assessed by assignment tests using
AFLPOP 1.0 (Duchesne and Bernatchez, 2002). This
programme enables the statistical determination of the
most likely source population of a given individual and
does not rely on complete population sampling within
the study area. The following settings were used: marker
frequencies of zero were replaced by (1/sample size þ 1),
the minimal log-likelihood difference to allocate an
individual was set to 1 (it was only allocated if its
allocation to a certain population was 10 times more
probable than to another population), and the number of
simulated genotypes to compute P-values was 500.
Results
Genetic diversity along successional time series
The three primer combinations yielded a 171 polymorphic AFLP fragments from a total of 184 reproducible markers in 378 individuals of T. pallescens. Average
gene diversity Ha was similar in populations (0.24–0.33;
mean±s.e. ¼ 0.28±0.03; Figure 2). No trend of either
0.34
Average gene diversity (Ha )
glacier valley, with extensive scree slopes on both valley
sides. The three glacier forelands contained accurately
dated chronosequences of moraines (Österreichischer
Alpenverein, Innsbruck, Austria; unpublished data) of
1 km (GB), 2 km (RM) and 2.5 km (LT) length, starting
with a terminal moraine dated to 1858 (Österreichischer
Alpenverein; unpublished data) and proceeding with
moraines from the years 1872 and 1923 and recently
deglaciated terrain from 1996 (Figure 1).
Pioneer communities on the youngest moraines exhibited a vegetation cover of 10–30% (Rudolph, 1991;
Wiedemann, 1991; Raffl et al., 2006b). While in RM valley
vegetation cover along the chronosequence increased to
almost 90% (Raffl et al., 2006b), it only proceeded to about
50% on the terminal moraines of 1858 in GB and LT
(Wiedemann, 1991; C Raffl, personal observation). T.
pallescens already occurred in the youngest stages of the
chronosequences of the three studied valleys and became
most prominent in the early successional stages, displacing
the pioneer communities after about 40 years (Raffl et al.,
2006b). It was absent from the valley slopes beyond side
moraines and was completely missing from the surrounding mountain ridges (Raffl and Erschbamer, 2004).
Samples were taken along the valley bottoms on
moraines representing the chronosequences (that is,
1996, 1923, 1871 and 1858). Material was also collected
from the side moraines at the basis of adjacent valley
slopes (Figure 1), with the exception of the NE-exposed
slope in GB and the SW-exposed slope in RM, where T.
pallescens did not occur. In LT, no samples could be taken
from the glacier stage of 1871, since the corresponding
moraine had been disturbed by flooding. Twenty-five
plants, at least separated by about 10 m, were randomly
sampled within a radius of about 300 m at each of the 16
sampling sites (Figure 1). Samples were dried in silica
gel. It was impossible to separate different populations
per moraine stage or slope site, respectively. Thus, the
collected 25 individuals per sampling site were pooled
and treated as populations during this study.
GB
RM
LT
0.32
0.30
0.28
0.26
0.24
0.22
1996
1923
1872
1858
Moraine stage
Figure 2 Average gene diversity Ha of Trifolium pallescens populations along successional series on three glacier forelands in the
Central European Alps. GB, Gaisberg valley; LT, Langtal valley;
RM, Rotmoos valley.
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C Raffl et al
529
increasing or decreasing gene diversity along the
chronosequences was observed (rs ¼ 0.080, P ¼ 0.200).
Similarly, no consistent trend was detected when considering values of Ha along the time series in each of the
three valleys alone (Figure 2). An initial decrease in gene
diversity in LT was opposed to an increase in GB and
RM. Subsequently, average gene diversity levelled out in
RM, while it increased in GB and LT with ongoing age of
the corresponding moraines.
Genetic differentiation among valleys and successional
stages
The AMOVA among valleys partitioned most of the
genetic variation to within populations (82.5%, Po0.001),
a smaller part to populations within valleys (12.9%,
Po0.001) and an only small, but still significant part
of variation to differentiation among valleys (4.5%,
P ¼ 0.039). The differentiation of stages was higher
(11.3%, Po0.001), while variation within populations
accounted for 84.6% (Po0.001).
A positive relationship between genetic and geographic distances among populations was present
(Mantel test; r ¼ 0.21, P ¼ 0.026) for the whole data set.
Similarly, a positive relationship of genetic and geographic distances was also apparent in each valley,
separately (RM: r ¼ 0.742, P ¼ 0.05; GB: r ¼ 0.701,
P ¼ 0.008; LT: r ¼ 0.408, P ¼ 0.05).
Source populations for the colonization of recently
deglaciated terrain
Recent gene flow between populations established on the
1996 deglaciated moraine and potential source populations was mainly restricted to gene flow within each of
the three valleys (Figure 3). At GB, the population on the
SW-exposed valley slope was assigned as the most likely
source population for 48% of the assigned multi-locus
genotypes compared to only 12% from the glacier
foreland. A more detailed analysis (data not shown)
identified 20 and 4% gene flow from the glacial stages of
1923 and 1858, respectively, to the recently deglaciated
terrain in GB, but none from the 1872 moraine. About
36% of the samples were unassigned at GB. At RM, the
populations along the valley bottom were identified
as the most likely sources of gene flow (45.8%; Figure 3),
with most stemming from the 1872 moraine (29.2%, as
compared to 4.2% from the 1858 moraine; data not
shown). One quarter of the individuals were not
assigned. At LT, the contribution of the remaining glacier
foreland to the individuals on the recently deglaciated
terrain was substantial (41.7%, Figure 3), but here gene
flow exclusively occurred from the 1923 moraine (data
not shown). In the LT valley, the SW-exposed slope was
assigned as another main source area for gene flow to the
recently deglaciated terrain (45.8%), while no gene flow
from the opposite valley slope was observed. About
12.5% of the individuals could not be assigned. No gene
flow from the NE-exposed slopes has been detected in
any of the three valleys studied.
The assignment test also identified some long-distance
gene flow events from LT into both, GB and RM
(Figure 3). There was 4% gene flow from the LT SWexposed slope to the pioneer stage of the glacier foreland
at GB. The SW-exposed slope from LT contributed 16.7%
gene flow to the recently deglaciated terrain in RM, while
the total glacier foreland of LT showed 12.5% gene flow
to the latter (Figure 3). There was no long-distance gene
flow, neither into LT nor between GB and RM.
Discussion
Development of genetic diversity in T. pallescens
populations on glacier forelands
Genetic diversity within T. pallescens populations from
three alpine glacier valleys was similar to those of other
LT-SW 4%
LT-SW
16.7%
SW 48%
1996
SW 45.8%
1996
1996
LT-GFL 12.5%
GFL 45.8%
GFL 41.7%
GFL 12%
GB
glacier
snout
RM
LT
Figure 3 Recent gene flow into pioneer populations of Trifolium pallescens on recently deglaciated terrain (1996 moraine) in three glacier
valleys in the Central European Alps. GB, Gaisberg valley; LT, Langtal valley; RM, Rotmoos valley; SW: south-west exposed slope; GFL,
glacier foreland without the population on the youngest moraine from 1996. Arrows indicate recent gene flow as identified by assignment
tests from the different source populations. From the 1996 moraine, 36, 25 and 12% of the individuals were unassigned in the GB, RM and LT
populations, respectively.
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Colonization of alpine glacier forelands
C Raffl et al
530
plant species from glacier forelands, namely, Geum
reptans (Pluess and Stöcklin, 2004) and Saxifraga aizoides
(Raffl et al., 2006a). No general trend in the development
of genetic diversity could be observed with increasing
population age along the chronosequence: The most
prominent feature was that genetic diversity only
slightly increased between the 1996 and 1872 stages,
but showed a substantial increase towards the 1858
moraine in GB (Figure 3). But, the pioneer populations of
T. pallescens on recently deglaciated terrain were not
characterized by a generally lower genetic diversity than
that found in populations of later successional stages in
all three glacier valleys studied (Figure 2). The glacier
forelands in GB and RM were also investigated in a
study on S. aizoides (Raffl et al., 2006a), where the
development of genetic diversity along the chronosequence was similar to that detected in T. pallescens. Our
results were in accordance with other studies indicating
more or less constant levels of intra-populational genetic
diversity through time (for example, Travis et al., 2002;
Erickson and Hamrick, 2003; Lian et al., 2003; Tremetsberger et al., 2003; Pluess and Stöcklin, 2004). This pattern
may be a consequence of gene dispersal, by either pollenand seed movement or inter-generation crosses within
populations, in T. pallescens favoured by its long lifespans and/or persistent seed banks (Gaudeul et al.,
2000).
Although diversity was mostly found within populations, there was a small, but significant, genetic differentiation of the populations of T. pallescens from different
valleys (4.5%). And there was a little larger significant
genetic differentiation of populations of different stages
along the successional series (11.3%). In accordance, we
found isolation by distance in each of the three valleys
studied separately and in the whole data set. Short seed
dispersal or pollen transport by insects is probably
responsible for the isolation by distance (Gaudeul et al.,
2000) observed within and between the valleys.
The above results clearly point to the important role
that gene flow plays (Whitlock and McCauley, 1990) in
recently colonized alpine habitats such as glacier forelands, where the total number of breeding individuals is
limited. (1) The weak isolation by distance observed and
the low, but significant, genetic differentiation of populations among different stages along the successional series
and among valleys are clear indications that gene flow
was not spatially unrestricted and not frequent enough
to eradicate population differentiation. (2) The high
initial genetic diversity detected in pioneer stages
suggests that even gene flow into newly established
populations seems substantial. Ibrahim et al. (1996)
highlighted the importance of rare long-distance dispersal for both, enhanced genetic diversity in and high
differentiation between founding populations. This is
consistent with the review by Pannell and Charlesworth
(2000), who emphasize the responsibility of gene flow
from remote sources for sufficient genetic variation in
newly established populations. (3) The steadily increasing genetic diversity in GB can be ascribed to continuous
gene flow via pollen and—to a smaller extent—seeds
from populations of T. pallescens on adjacent scree slopes.
In the RM valley, genetic diversity only exhibited a slight
increase in time. Unlike the situation in the GB valley,
gene flow from adjacent slopes is limited because of
the lack of adequate habitats of T. pallescens in alpine
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grasslands occupying the valley slopes (Raffl and
Erschbamer, 2004). However, estimates of present-day
gene flow based on the actual pattern in genetic diversity
may be considered cautious since gene frequency
differences that arise during founding events may persist
for many generations (Ibrahim et al., 1996).
Besides environmental differences, species-specific
ecological requirements also determine patterns of
genetic diversity (Tremetsberger et al., 2003). Most alpine
plants are capable of clonal reproduction in response to
the harsh and unpredictable environmental conditions
aggravating successful seedling establishment (Niederfriniger-Schlag and Erschbamer, 2000). Accordingly, also
in T. pallescens, vegetative reproduction via tillers may
contribute to enhanced genetic differentiation among
populations. However, for the maintenance of genetic
diversity within populations, the establishment of seedlings is important (Booy et al., 2000). Thus, the observed
increase of diversity on older moraines may be also
enhanced because the effective population size was
sufficient for successful sexual reproduction in T.
pallescens not until the 1872 stage. The pioneer S. aizoides,
which was almost suppressed in older successional
stages, exhibited a contrary progression of genetic
diversity (Raffl et al., 2006b).
Potential source populations for the colonization of the
recently deglaciated terrain
Several sources of gene flow to the populations of T.
pallescens on recently deglaciated terrain were identified.
The results by Lian et al. (2003) indicated two sequential
modes of seed dispersal for population establishment;
while pioneers may stem from seeds dispersed over long
distances, the further establishment tends to base on
short-distance dispersal of the nearest mother plant.
For T. pallescens, the adjacent glacier foreland was
generally the most important source for gene flow into
populations on recently deglaciated terrain in LT (41.7%)
and RM (45.8%), but this proportion was much lower in
GB (12%; Figure 3). Although potential source populations were rare for T. pallescens on adjacent valley slopes
(Raffl and Erschbamer, 2004), they provided almost as
much gene flow to pioneer populations as populations
on the glacier foreland (except in RM). In GB, gene flow
from valley slopes accounted for 48% and for 45.8% in
LT. In contrast to this situation, in T. pallescens, gene flow
to recently deglaciated ground from a much larger
potential source area was detected in S. aizoides including
surrounding mountain ridges (Raffl et al., 2006a).
Despite the high mountain ridge in-between them,
recent gene flow from LT into GB (4%) and from RM
(29.2%) valley was found (Figure 3). In the only other
study that investigated recent long-distance gene flow in
an alpine plant, gene flow among populations from
different valleys (4%) was also found (Raffl et al., 2006a).
Rare long-distance dispersal can dramatically increase
gene flow during colonization (Nichols and Hewitt,
1994). According to Le Corre and Kremer (1998) the main
effect of large-distance dispersal is to reduce both, the
loss of diversity and the increase in genetic differentiation by preventing a pronounced effect of founder
events. Thus, even low rates of long-distance dispersal
potentially play an important role in the population
dynamics of T. pallescens. Despite its attribute of small
Colonization of alpine glacier forelands
C Raffl et al
531
dispersibility (Stöcklin and Bäumler, 1996; Niederfriniger-Schlag and Erschbamer, 2000), the present genetic
results suggest that the comparably large seeds of T.
pallescens are nevertheless regularly dispersed over
relatively large distances. This adds up to the growing
body of genetic studies on recent or contemporary gene
flow that finds much higher rates and longer distances of
gene flow than that suggested by traditional ecological
experiments (Nathan, 2006).
Conclusions
This study of genetic diversity on three alpine glacier
foreland populations in the European Alps has given
insights on probable origins of colonizing T. pallescens.
There was recursive gene flow among populations
sometimes even over larger distances. This led to
substantial genetic diversity even in the youngest
populations, representing a genetic sample from different source areas. Pioneer populations were not a genetic
sub-sample of the yet established populations on the
glacier foreland only. However, gene flow was not
spatially unrestricted as indicated by a weak local
isolation by distance pattern. No general trend in the
development of genetic diversity was observed with the
increase of plant population age. The actual patterns are
a result of the combination of factors, such as gene flow
and growth rate, influenced by site- and species-specific
attributes.
Acknowledgements
We acknowledge the help in the field and laboratory
as well as the advice by M Blassnig, W Durka,
E Grasserbauer, F Gugerli, M Hubmann, A Juen,
H Kudrnovsky, B Lorbeg, S Mantsch, P Schönswetter,
E Schwienbacher, M Traugott and M Wallinger. We also
thank three anonymous referees for their valuable
comments on the paper. This work was financially
supported by the Austrian Science Fund (FWF; project
no. P14811-B06).
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